Avengers #1, September 1963
Synopsis: Loki wants revenge on his half-brother Thor. He schemes to frame the Hulk in an accident with the belief that the Thunder God will come to investigate. The Teen Brigade (with member and Hulk associate Rick Jones) call on the Fantastic Four for help, but the message is heard by other heroes, namely Iron Man, Ant-Man & the Wasp, and Thor himself. All unite to bring down the Hulk, but Thor soon brings back to Earth his half-brother and the evil plan is revealed. Before everyone leaves, Ant-Man makes the suggestion that by working together, all five heroes could do much good. It is agreed to form a new group named the Avengers.
Since the Justice League of America was enjoying good popularity at DC, Stan Lee decided to create a new team of super-powered beings... and the history of comic books would instantly change. The existence of the Avengers was the ultimate consolidation of the Marvel Universe as we still know it, where many heroes from other titles became permanent characters in a second one. These were not just guest-starring stories. Thor had been around since Journey Into Mystery #83; Iron Man from Tales of Suspense #39; Hulk from Hulk #1; Ant-Man (as Hank Pym) from Tales to Astonish #27 and the Wasp from Tales to Astonish #44. Together, they became the Avengers at the suggestion of Ant-Man. The very name ?Avengers? comes from the imagination of the Wasp. It's fascinating to note how much these characters were so different from each other, in talent and personality and yet, still decided to become partners. All take part in the action, with the winsome Wasp considered a bit of a mascot...
Why would these people agree to form a team? In Iron Man's case, a sense a justice and probably an opportunity to get to know other heroes. For Thor, the chance to work besides humans of great courage and learn something about human behavior. Ant-Man? It will be revealed later that he was seeking comfort in others, but found himself feeling inadequate in his small form, so he created the Giant-Man persona soon after. As for the Wasp, at that point, she was following Ant-Man everywhere (and was surely amused at the prospect of innocently flirting with Thor...). Lastly, can we consider that the Hulk was seeking, in a subconscious level, some sort of sense of belonging?
Their first adversary was Loki, brother of Thor, who at this point was probably the most featured villain in the Marvel Universe in term of appearances. He would continue to this day to be haunted by his actions in this story, where he sets in motion the events for the creation of the Avengers, no less! This is one of the better tales of the early days at Marvel, with seemingly no weak points and an effortless flow of dynamic action. Of course, the main interest lies in observing these various personalities interacting together, which would pave the way for many internal conflicts and in-fighting for years to come.